Acoustic drilling method and apparatus



May 17, 1966 w. B. BROOKS ACOUSTIC DRILLING METHOD AND APPARATUS Filed June 18, 1962 FIG. 3

FIG. 4

MOTOR 1 ELECTRIC FIG. 2

FLUID TURBINE MOTOR F I G. I

FIG. 5

United States Patent 3,251,424 ACOUSTIC DRILLING METHOD AND APPARATUS Warren B. Brooks, Dallas, Tex., assignor to Socony Mobil Oil Company, Inc., a corporation of New York Filed June 18, 1962, Ser. No. 203,085 3 Claims. (Cl. 17556) This invention relates to a method and apparatus for drilling a borehole in the earth. More specifically, this invention rel-ates to a method and apparatus for drilling a borehole by means of fluid jet streams.

At the present time, the most commonly used method of drilling a borehole in the earth, particularly in the oil industry, is one which is referred to as rotary drilling. In rotary drilling, a drill bit having cutting surfaces is rotated in contact with the rock in an earth formation by means of a long column of drill collars and'drill pipe which are powered by various types of equipment positioned on the surface of the earth. Other methods of drilling have been suggested and some are currently being used, but essentially all of them require a drill bit. A major disadvantage of and consequently one of the most expensive aspects of rotary drilling and most of the other presently employed methods is the necessity of changing the drill bit at frequent intervals. This obviously requires that all of the drill pipe and drill collars be removed from the borehole, the bit changed, and the drill pipe and drill collars again reinserted into the borehole before drilling can again commence.

It is one object of the present invention to provide a method and apparatus for drilling a borehole wherein a drill bit is not employed. It is another object of the present invention to provide a method and apparatus for drilling a borehole in which fluid jets are employed for the purpose of advancing the borehole through the earth.

In accordance with the present invention, drilling fluid is directed downwardly through a borehole toward the bottom thereof, the drilling fluid is formed into one or more jet streams, alternating high and low acoustic pressure pulses are generated within each of the jet i 3,251,424 Patented May 17, 1966 ruptions of the fluid movement within the jet streams that can be considerably larger than the hydrostatic pressure within the fluid. The jet streams in which the alternating acoustic pressure pulses are generated are then directed against the bottom of the borehole for the purpose of eroding away the rock and other materials comprising the earth formation being drilled.

The method of the invention may be carried out by several different forms of apparatus, including those i-llustrated in the drawing. Referring specifically to FIG- URES l and 3, a fluid turbine type motor 10 is secured to the lower end of a string of drill pipe, not shown. The fluid turbine motor may be any one of several currently available to the industry. Examples of fluid turthine motors which may used are shown at page 3478, volume 2, and page 4845, volume 3, of The Composite Catalog of Oil Field Equipment and Services, 24th (1960-61) Revision, published by World Oil, Houston, Texas. Other examples of fluid turbine motors which may be employed are shown in US. Patent 2,908,534 to H. Rietsch, US. Patent 2,963,099 to S. J. Gianelloni,

Jr., and at pages B-39 through B-44 of the October 1956 issue of the Petroleum Engineer.

Secured to the lower or outlet end of outer casing '11 of fluid turbine motor 10 is a fixed or stationary valve plate 12. Valve plate 12 is provided with a plurality of apertures or openings 13. Secured within the lower or outlet end of turbine rotor 14 is a rotatable valve plate 15 which is provided with a plurality of apertures or openings 20. Openings 20 in valve 15 plate cooperate with openings 13 in valve plate 12 to separate the drilling fluid flowing through the turbine rotor 14 into a plurality of fluid jets. As rotor 14 is rotated, openings 20 streams, and each of the jet streams is directed against the bottom of the borehole to effect drilling of the earth formation.

In the drawing;

FIGURE 1 diagrammatically illustrates, in partial cross section, one embodiment of' apparatus which may be utilized to carry out the present invention.

FIIGUR E 2 shows in cross section another embodi-- ment of the apparatus of the invention.

FIGURE 3 is a partial perspective view of one portion of the apparatus illustrated in FIGURE 1.

FIGURES 4 and 5 are views in cross section of modifica-tions which may be made in the apparatus illustrated in both FIGURES 1 and 2.

In carrying out the method of the invention, a drilling fluid, which may be either water or a mixture of a liquid and various solid materials generally referred to as drilling mud, is directed through a confined flow path along the length of a borehole toward the bottom thereof. At

or near the lower end of opening of the flow path, the

drilling fluid is formed into one or is separated into a plurality of relativey high velocity jet streams. Within each of the jet streams, a series of succession of alternating high and low acoustic pressure pulses are generated. Each of these acoustic pressure pulses comprises a dynamic pressure effected by means of sudden interpass in and out of registry with openings 13, causing starting and stopping of the fluid-jets to generate a succession of alternating high and low acoustic pressure pulses within the fluid jet streams. The positioning, number, and relationship of openings 20 and openings 13 will be discussed in further detail hereinafter. Valve plates 12 and 15 are positioned as close together as practicable with the distance between them being only that necessary to prevent undue friction between the plates due to the rotation of the plate 15. In order to maintain correct alignment and positioning. of plates 12 and 15 relative to each other, it may be desirable to provide some form of bearing, not shown, between the plates. Such a hearing, if necessary, might rest between the plates along their center line.

The actual drilling of a borehole by the method and apparatus disclosed herein is accomplished by the efiect of the fluid jet streams produced by the drilling fluid passing through openings 20 and 13 in the valve plates. The number of jet streams, their placement, and-the magnitude and frequency of the acoustic pressure impulses generated within the jet streams are dependent in part upon the positions, sizes, and number of the openings in the valve plates, together with the rotational speed of the movable valve plate. In one embodiment, the openings in each of the valve plates are arranged uniformly about concentric circles; as illustrated in FIGURES 1 and 3, with the holes in each of the valve plates being so positioned that for a given'position of rotation of movable valve plate 15 relative to stationary valve plate 12 holes 20 will 'be in exact registry 'with holes 13, causing simultaneous separation of the drilling fluid into a plurality of jet streams covering substantially the entire lower end of the drilling tool. In this form, the frequency of the alter- 3 nating acoustic pressure pulses generated within any particular jet stream flowing from the drilling tool is dependent upon the number of openings in the rotatable valve plate which pass into registry with an opening in the stationary valve plate during a complete rotation of the movable valve plate. The frequency of the alternating acoustic pressure pulses may be determined from the formula f-znr where f=nr=30 30=900 cycles per second The actual acoustic pressure developed within each of the fluid jets is determined in accordance with the equation where P=the acoustic pressure,

=the density of the drilling fluid,

C =the velocity of sound in the drilling fluid,

V=the change in velocity of the fluid due to operation of the mechanism, and

g acceleration due to gravity.

For a particular tool designed with holes sized to effect fluid flow therethrough of 100 feet per second and utilizmg water as the drilling fluid, the approximate pressure obtainable will be 0.036 lb./in. 5000 ft./sec. 1200 in./see.

P 32.2 ft./sec./sec.

In considering hole placement and design in the valve plates, it will be obvious that there may be numerous different patterns of fluid jets, frequencies, and combinations whereby the jets are either in phase with each other or out of phase. Obviously, a fluid jet is created only when a hole 20 in movable valve plate comes into registry or partial registry with a hole 13 in fixed valve plate 12. The total number of fluid jets available for drilling is dependent upon the number of holes provided in the lower or fixed plate 12, while the frequency of the acoustic pressure pulses generated within a fluid jet stream is dependent upon the number of holes in the movable plate 15 which register with any one hole in plate 12 during a revolution of the movable plate. Considering the above-discussed formulas, the frequency of the acoustic impulses generated within a fluid jet stream may readily be varied by changing the number of holes in the movable plate while the magnitude or amplitude-of the acoustic pressure pulses may be controlled by the sizing of the holes which affect the velocity of the drilling fluid through the holes. If the same number of holes is placed in the inner circle as in the outer circle and the holes are placed at the same angle about the plates, the frequencies of the acoustic pressure pulses generated within the fluid jet streams will be the same for all of the jet streams. On the other hand,

by making the number of holes in the inner concentric circle different from the number in the outer concentric circle and varying their angular position about the plates, it is obvious that the frequencies of the acoustic impulses generated in the fluid jets coming from the holes in the two =6700 p.s.i.

4 circles will be different and they also will be out of phase with each other.

In carrying out the method of the invention, a drilling tool as illustrated in FIGURE 1 is secured to the lower end of a string of conventional drill pipe, not shown, and the drilling tool is lowered in a conventional manner into the borehole. Drilling fluid, which may be water or any other form of drilling fluid desired, is pumped through the drill string into the fluid turbine motor. The drilling fluid passes through the turbine of the fluid turbine motor, causing the turbine rotor 14 to rotate at the particular speed for which the tool is designed. The drilling fluid passes through the rotor 14, toward valve plate 15 which is secured to and rotates simultaneously with the rotor 14. As the holes 20 in valve plate 15 are rotated into registry with the holes 13 in fixed valve plate 12, a plurality of flu-id jet streams are created. By positioning the drilling tool in the proximity of the bottom of the borehole, the fluid jet streams are directed against the bottom of the borehole, causing the failure of the formation. As the formation fails due to the acoustic energy from the fluid jet streams, the cuttings, as they are generally referred to, are washed out by the drilling fluid and passed upwardly in the annulus, around the fluid turbine motor and the string of drill pipe, back to the surface. As the rotor 14 continues rotation, the holes 20 will pass out of registry with the holes 13, effecting sudden stoppage of the flow of drilling fluid through the valve plate; and, of course, with further rotation of the rotor 14, the holes will again pass into registry with the sudden opening of the holes, causing the sudden creation again of the fluid jet streams. Obviously, with the alternate opening and closing of the holes, the fluid jet streams are not only created, but alternating acoustic pressure pulses are generated within the fluid jet streams with the amplitude or magnitude of the acoustic pressure pulses alternating above and below the hydrostatic pressure of the fluid within the drilling tool. The alternating high and low acoustic pressure pulses generated within the jet streams will more effectively erode away the formation than the steady fluid streams employed in previously used jet drilling tools.

Another form of apparatus which may be employed in carrying out the method of the invention is illustrated in FIGURE 2. With respect to this particular embodiment of the apparatus of the invention, the description thereof will employ identical reference numerals to those used in connection with FIGURE 1 for parts functioning identically to those shown in FIGURE 1. Outer tool casing 30 is provided at its upper end with threads 31 to permit connection to the lower end of a string of conventional drill pipe. Secured at the lower end or discharge end of casing 30 is a fixed or stationary valve plate 12 which is provided with apertures or holes 13. Casing 30 serves not only as the outer casing for the tool and support member for the stationary valve plate, but also functions to define a flow path for drilling fluid through the tool toward the stationary valve plate. Supported within outer casing 30' on spokelike brackets 32 is an electric motor 33 which is a relatively long, slender type motor having an outer diameter sufliciently less than the internal diameter of outer casing 30 to provide ample space between the motor and the inside of the casing to permit flow of drilling fluid through the tool around the motor. Supported on motor shaft 34 is a rotatable valve plate 15 which is provided with a plurality of apertures or openings 20. The description and function of both valve plate 12 and valve plate 15 are identical to those given hereinabove in connection with the discussion of the apparatus illustrated in FIGURE 1. Electric motor 33 serves to rotate valve plate 15 to generate a succession of alternating high and low acoustic pressure pulses within the drilling fluid flowing through the tool in the manner described above. Electriccurrent may be conducted to electric motor 33 by any of the conventional means employed in operating down hole electric motors.

Illustrated in FIGURES 4 and 5 are variations in the design of the lower stationary valve plate 12 which may be made for the purpose of changing the operating characteristics of either of the tools illustrated in FIGURES 1 and 2. In the apparatus illustrated in both FIGURES 4 and 5, the upper rotatable valve plate 15 remains unchanged. Referring specifically to FIGURE 4, lower stationary valve plate 12 is modified by providing over each of the holes therethrough a nozzlelike extension 40 which has a progressively decreasing cross section for the purpose of increasing the velocity of the fluid passing through a hole and its associated nozzle member. By increasing the fluid velocity through the hole and its associated nozzle member, the alternating acoustic pressure is increased as will be obvious from a re-examination of the formula discussed above on which this pressure is based. Since the alternating acoustic pressure obtainable is directly proportional to velocity, by increasing the velocity with nozzle members 40 the alternating acoustic pressure is increased.

The modification of plate 12 as illustrated in FIGURE 5 is designed with varying length nozzles such that a stairstep type hole is drilled. A further feature of the apparatus illustrated in FIGURE 5 is that the formation is simultaneously subjected to positive and negative acoustic pressures on adjacent areas of the bottom of the formation below the jet nozzles. The nozzles 45 which comprise the outer row of nozzles on the fixed valve plate may be of any length and cross-sectional area desired. Nozzles 46 which make up the second row of nozzles adjacent to the row of nozzles 45 are, however, longer than nozzles 45 by a distance a which is equivalent to one-half of the wave length of the acoustic pressure pulses generated Within the jet streams. The length of nozzles 46 relative to nozzles 45 may be readily determined in accordance with the following formula:

where f=the frequency of the alternating acoustic pressure pulses generated by the drilling tool,

7t=the wave length of the acoustic energy generated,

and

C=the velocity of sound in the drilling fluid being used in the tool.

By way of illustration, using water as a drilling fluid and assuming a drilling tool constructed in accordance with the invention produces fluid jets having acoustic pressure pulses generated therein at a frequency of 2500 cycles per second, the distance d may be determined as follows:

Therefore, when nozzles 46 are constructed to be one foot longer than nozzles 45, the acoustic pressure pulses generated in nozzles 45 and 46 will be out of phase one-half wave length from each other. In other words, when the acoustic pressure pulse in the fluid jets from nozzles 45 is at a maximum on the positive side, the acoustic pressure pulse in the fluid jets from nozzles 46 will be at a maximum on the negative side. In order for the acoustic pressure pulses in the jets produced by nozzles 47 to be one-half wave length out of phase with those from nozzles 46, it will be obvious that nozzles 47 will be longer than nozzles 46 by a distance equal to one-half the wave length which, in the above example, is one foot. Ob viously, other combinations of phase relationships between the acoustic pressure pulses generated by the various nozzles may be obtained by adjustment of the lengths of the nozzles. It may be observed that in connection with the stairstep type nozzle arrangement as shown in FIGURE 5, the making of the nozzle lengths one-half wave length difference in distance for adjacent rows of frequency ranges. This is because of the unwieldlylengths of nozzles which would be required in the lower frequency ranges. For example, in the above example the nozzles lengths difler by one foot for a 25 00cycle per second frequency, and if this were reduced to 1000 cycles per second frequency the nozzle lengths would vary by 2 /2 feet. Obviously this can reach an impractical limit.

Another means of subjecting adjacent portions of the bottom of the hole to high and low values of acoustic pressure is by designing the rotating plate such that adjacent holes are not in registry at the same time, as mentioned previously.

While the apparatus of the invention has been illustrated in terms of various embodiments of a combination of a. fixed and a rotating valve plate, it will be obvious that other forms of apparatus may, be employed for the purpose of generating acoustic pressure pulses within the fluid jet streams developed by the apparatus. For example, movable valve plate 15 rather than being rotated relative to valve plate 12 might be a sliding, eccentrically driven valve plate. Such a sliding valve plate might be powered through an eccentric by either electric or fluid turbine motor means and may be provided with one or more openings. Also, it will be obvious that while downhole motor means have been illustrated herein and are to be preferred, it would be possible to actuate a valve plate such as rotatable valve plate 15 by mechanical means from the surface of the earth, such as by a shaft extending down through the drill string to the valve plate. Other means for generating acoustic pressure pulses within fluid jets will, of course, occur to those skilled in the art.v

What is claimed is: 1. In a method of drilling a borehole the steps which comprise (a) conducting a stream of drilling fluid along a borehole toward the bottom thereof; (b) separating said drilling fluid into a plurality of .jet

streams; (e) generating within one portion of said jet streams alternating high and low pressure acoustic pulses; (d) generating within another portion of said jet streams high and low pressure acoustic pulses, said acoustic pulses being out of phase relationship with the acoustic pulses generated during step (c); and (e) directing said jet streams against the bottom of said borehole. 2. In apparatus for fluid jet drilling the combination which comprises (a) conduit means for conducting drilling fluid through a borehole toward the bottom thereof;

(b) a fixed plate secured across said conduit means near the lower end thereof, said plate being provided with a plurality of openings to divide said drilling fluid into jet streams and direct said jet streams against the bottom of said borehole;

(c) a nozzle element secured over each of said openings in said fixed plate to increase the velocity of said jet streams;

.(d) a rotatable plate positioned above and adjacent to said fixed plate, said rotatable plate being provided with a plurality of openings adapted to register with said openings in said fixed plate at a given position of rotation of said rotatable plate relative to said fixed plate; and

(e) power means connected to said rotatable plate for rotating said plate relative to said fixed plate.

3. In the apparatus of claim 2 wherein (a) the openings in said fixed plate and said rotatable plate are arranged in concentric circular rows around the centers of said plates; and

(b) the length of the nozzle elements over each of said rows of openings in said fixed plate differs from the length of the nozzle elements over an adjacent row of openings by a distance equal to one-half the wave 

1. IN A METHOD OF DRILLING A BOREHOLE THE STEPS WHICH COMPRISE (A) CONDUCTING A STREAM OF DRILLING FLUID ALONG A BOREHOLE TOWARD THE BOTTOM THEREOF; (B) SEPARATING SAID DRILLING FLUID INTO A PLURALITY OF JET STREAMS; (C) GENERATING WITHIN ONE PORTION OF SAID JET STREAMS ALTERNATING HIGH AND LOW PRESSURE ACOUSTIC PULSES; (D) GENERATING WITHIN ANOTHER PORTION OF SAID JET STREAMS HIGH AND LOW PRESSURE ACOUSTIC PULSES, SAID ACOUSTIC PULSES BEING OUT OF PHASE RELATIONSHIP WITH THE ACOUSTIC PULSES GENERATED DURING STEP (C); AND (E) DIRECTING SAID JET STREAMS AGAINST THE BOTTOM OF SAID BOREHOLE. 